Roller vane pump incorporating a bearing bush

ABSTRACT

Roller vane pump, in particular suited for pumping fluid in a continuously variable automatic transmission of a motor vehicle, provided with a pump housing accommodating a substantially cylindrical carrier, which is rotatable about a central axis, and a cam ring encompassing the carrier in the radial direction, whereby a radial clearance between the carrier and the cam ring varies along a circumference of the carrier, and with a pump shaft extending co-axial with said central axis through the carrier, characterised in that there is provided in the pump housing a bearing bush having an essentially cylindrical central bore through which the pump shaft extends.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a roller vane pump and in particular toa roller vane pump suited for pumping fluid in a continuously variableautomatic transmission (CVT) for motor vehicles. Such a roller vane pumpis known from the European patent 0.921.314 and is intended for pumpingautomatic transmission fluid in hydraulically controlled and/or operatedcontinuously variable transmissions for motor vehicles. Particularly ina belt-and-pulley type CVT, a large flow of fluid at a high pressure maybe required for control of the transmission. The known pump may beprovided with several pump units, whereby a pump unit is a functionalpump unit, i.e. having a suction section where fluid is drawn into thepump and a discharge section where fluid is discharged from the pump.Since the pump is usually driven by a main drive shaft of the vehicle,it is designed to be able to provide a desired pump yield, i.e. adesired flow of fluid, even at a lower most rotational speed of thedrive shaft, e.g. idle speed. At the same time, the pump is designed toreliably withstand prolonged operation at an upper most rotational speedof the drive shaft.

[0002] The known pump is provided with a pump housing accommodating asubstantially cylindrical carrier, which is rotatable about a centralaxis, and with a cam ring encompassing the carrier in the direction,whereby a clearance in the radial direction between the carrier and thecam ring varies along a circumference of the cam ring. The carrier isprovided with a number of slots extending inwardly from the radiallyouter surface of the carrier, at least some of which slideablyaccommodate a roller element. The carrier is rotatable by means of apump shaft extending co-axial with said central axis through thecarrier. The pump shaft is supported in the housing on axial sides ofthe carrier, whereby the housing provides a bearing surface for the pumpshaft. A small gap exists between the carrier and the pump housing as aresult of an axial clearance introduced there between, which gap allowsthe carrier to rotate with respect to the housing. The gap furtherenables a lubrication flow from the discharge section of a pump unit tothe bearing surface for lubrication thereof. It is noted that, as aconsequence, the gap also enables a leakage flow from the high-pressuredischarge section to the low-pressure suction section, which affectspump efficiency. Usually, said axial clearance will, therefore, be setas little as possible given a desired amount of lubrication.

[0003] The known pump has the disadvantage that the carrier may slightlytilt with respect to the pump housing under the influence of forinstance mechanical shocks, changes in the rotational speed or changesin the fluid pressure at the discharge section. Particularly, when thepump shaft is relatively long a substantial movement of the carrier mayoccur. A rotation of the carrier causes said gap to vary along itscircumference. At a location where said clearance is large, said leakageflow will also be large, whereby the -volumetric- pump efficiency isdisadvantageously affected, whereas at a location where said clearanceis small, possibly even non-existent, friction between the carrier andthe housing is high, whereby the -mechanical- pump efficiency is againdisadvantageously affected. At a location where said gap isnon-existent, wear of the pump housing and of the carrier may alsobecome a problem.

[0004] The above mentioned disadvantage of the known pump isparticularly relevant when the pump housing is made of a light weightand/or soft material, such as aluminium, which is generally also aductile material and/or when the carrier is rigidly fixed to the pumpshaft. In such cases, said movement of the carrier may occur withrelative ease, causing the width of said gap to change considerablyalong the circumference of the carrier. It is an object of the presentinvention to improve the pump efficiency of the known roller vane pump.

SUMMARY OF THE INVENTION

[0005] According to the invention this object is achieved with theroller vane pump, wherein there is provided in the pump housing abearing bush having an essentially cylindrical central bore throughwhich the pump shaft extends. In the pump according to the inventionthere is provided a separate bearing bush, which bearing bushaccommodates the pump shaft in the pump housing and provides a bearingsurface for the rotation of the said shaft. The provision of the bearingbush stiffens the construction of the pump shaft and thereby reducessaid movement of the pump shaft.

[0006] In a further development of the invention, the bearing bush ismade of material a less ductile than aluminium, such as copper. It isfurther preferred that the bearing bush tightly fits around said pumpshaft in the radial direction. Both features have the advantage that thefreedom of movement of the pump shaft is restricted. It may also beadvantageous to provide a bearing bush on either axial end of thecarrier. In this manner a stable configuration of the pump housing, thepump shaft and the carrier is achieved.

[0007] According to the invention it is advantageous, if the bearingbush is provided with a lubrication groove on a radially inner surfacethereof, preferably having a substantially elongated shape with a longaxis, for allowing a fluid to penetrate between the bearing bush and thepump shaft. To this end the lubrication groove may start at an axial endof the bearing bush closest to the carrier and continues with its longaxis oriented in a direction having an axial component. The lubricationgroove allows a flow of lubrication fluid in between the pump shaft andthe bearing bush, even if the bearing bush fits relatively tightlyaround said shaft. The lubrication groove may span the entire axiallength of the bearing bush. However, to prevent substantial fluidcommunication with the environment, it is preferred that the lubricationgroove ends at some distance from the axial end of the bearing bushopposite said axial end of the bearing bush closest to the carrier. Whenthe lubrication groove is oriented at an angle with respect to the axialdirection, the lubrication fluid is distributed over at least a part ofa circumference of the pump shaft. For optimum distribution of thelubrication fluid, the said angle is set such that the lubricationgroove extends in the direction of rotation of the pump shaft.

[0008] As mentioned in the above, the pump is provided with one or morelow pressure suction sections and one or more high pressure dischargesections, which sections are located alternately along the circumferenceof the cam ring. When said pressures are unevenly distributed along saidcircumference, a net-force acts on the carrier and on the pump shaft ata specific tangential location, which net-force urges the pump shaft ina generally radial direction. Thus, when the pump is provided with asingle pump unit, or when the pump units have mutually differentdischarge pressures, a contact pressure between the pump shaft and thebearing bush is unevenly distributed in dependence on tangentialposition and varies between a highest level, at a tangential positionsubstantially opposite a tangential position of the discharge sectionhaving the highest discharge pressure, and a lowest level, at atangential position substantially corresponding to the tangentialposition of the discharge section having the highest discharge pressure.According to the invention, it is in such cases to be preferred that thelubrication groove is predominantly located in a region of tangentialpositions where the said contact pressure is relatively low, so thatthere is no need to disturb the contact between the pump shaft and thebearing bush at the location where the said contact pressure is thehighest.

[0009] In a further elaboration of such embodiment, the lubricationgroove starts at a tangential position of the discharge section wherethe prevailing pressure is at a maximum, whereby a tangential positioncorresponding to a central part of the said section is particularlysuitable. If in such a case the long axis of the lubrication groove isoriented at an angle with respect to the axial direction, it ispreferable that either one or both of a length of the lubrication grooveand of said angle are chosen such that it extends in the tangentialdirection over an angle which approximately corresponds to π minus ½πdivided the number of pump units of the pump. This measure effects thatthe lubrication groove does not extend into the region of tangentialpositions where the said contact pressure is the highest.

[0010] In yet a further development of the pump according to theinvention, the bearing bush is provided with a distribution groove onits inner surface having a substantially elongated shape with a longaxis that is oriented substantially axially and that intersects the longaxis of the lubrication groove, for further improving the distributionof the lubrication fluid. The distribution groove may extend over asubstantial part of an axial dimension of the bearing bush. It is,however, to be preferred if there remains a distance of at least ¼ ofthe said axial dimension between an axial end of the bearing bush and ofthe distribution groove so as to limit communication of lubricationfluid between the distribution groove and the environment.

[0011] The invention will now be explained in greater detail withreference to the non-restricting examples of embodiment shown in thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the drawings:

[0013]FIG. 1 is an axial cross section of the known roller vane knownpump taken at an axial position immediately adjacent to the carrier;

[0014]FIG. 2 is a tangential cross section of the known pump;

[0015]FIG. 3 is a tangential cross section of a roller vane pumpaccording to the invention;

[0016]FIG. 4 is a perspective view of a bearing bush for the roller vanepump according to the invention;

[0017]FIG. 5 is a plane view of the inner surface of a bearing bushaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018]FIGS. 1 and 2 respectively provide an axial cross section and atangential cross section of the known roller vane pump. The known pumpcomprises a pump housing 12 that is composed of three pump housing parts1, 8 and 9, which can be secured to each other by means of bolts (e.g.bolt 25 shown in FIG. 3) that are inserted in holes in the pump housing12, e.g. hole 10. The central pump housing part 1 accommodates anessentially cylindrically shaped carrier 4, which is rotatable about acentral axis 4 a in a direction of rotation indicated by the arrow bymeans of a pump shaft 5, and a cam ring 2 with a radially inwardoriented cam surface 2 a, which cam ring 2 radially encompasses thecarrier 4, whereby a clearance C in the radial direction between thecarrier 4 and the cam ring 2 varies along the circumference of the camring 2. On its periphery the carrier 4 is provided with radiallyinwardly extending slots 6 that accommodate essentially cylindricallyshaped roller elements 7. The roller elements 7 are accommodated in theslots 6, such that they are able to slide in a predominantly radiallyoriented direction. The pump shaft 5 extends in axial direction throughthe carrier 4 and, on either axial side thereof, is supported in thepump housing 12, whereby the housing 12 provides a bearing surface. Thepump shaft 5 is fixed to the carrier 4 by means of a wedge 3.

[0019] During operation of the pump, the carrier 4, the cam ring 2, andthe roller elements 7 define a number of pump chambers 13 that are boundin axial sense by the inner surfaces 23 and 14 of the outer pump housingparts 8 and 9 respectively and that may arrive in communication with asupply line 24 in the pump housing 12 for hydraulic fluid, through oneor more of a number of supply ports 11 and 16 and which may arrive incommunication with a discharge line (not shown) in the pump housing 12for hydraulic fluid, through one or more of a number of discharge ports17 and 18. When the carrier 4 is rotated during operation of the pump, asurface area of the pump chambers 13 as seen in axial cyclicallyincrease and decrease, as can be deduced from in FIG. 1. Accordingly, avolume of the pump chambers 13 also cyclically increase and decrease, sothat, on the one hand, fluid sucked from the supply line into the pumpchamber 13 when its volume increases, i.e. at the location of aso-called low pressure pump section L, and, on the other hand, fluid ispressed out of the pump chamber 13 when its volume decreases, i.e. atthe location of a so-called high pressure pump section H.

[0020]FIG. 3 is a tangential cross section of an embodiment of theroller vane pump according to the invention. In this figure similar pumpparts are provided with the same reference numeral as provided in FIGS.1 and 2. On either axial side of the carrier 4, there is provided abearing bush 30 in the pump housing 12 through which the pump shaft 5extends in the axial direction. The bearing bushes 30 provide a bearingsurface for the rotation of the pump shaft 5 and also stiffen theconstruction of the pump. At an axial end 33 of the bearing bush 30closest to the carrier 4, the bushes 30 are provided with a hook part 38that is formed by a radially outwardly oriented thickening thatinteracts with the pump housing 12 to prevent the bushes 30 from axiallymoving with respect to the pump housing 12. Lubrication fluid isprovided to a gap (not shown) between the radially inner surface of thebushes 30 and the radially outer surface of the pump shaft 5 from anessentially annular cavity 39 within the pump housing 12. Here saidcavity 39 is bound by the carrier 4, the pump shaft 5 and the bearingbush 30. In the cavity 39 there exists an elevated fluid pressure as aresult of a leakage flow from the pump chambers 13, in particular thechambers 13 at the location of a high pressure pump section H, to thecavity 39. This leakage is enabled by a small gap (not shown) betweenthe housing 12 and the carrier 4, which gap allows the carrier 4 torotate in the housing 12. The annular cavity 39 advantageously forms areservoir for lubrication fluid at an elevated pressure, from whichcavity 39 the interface between the pump shaft 5 and the bushes 30 isreliably provided with lubrication.

[0021]FIGS. 4 and 5 are two views of an embodiment of the bearing bush30, whereby FIG. 4 is a perspective view and FIG. 2 is a plane view of aradially inner surface of the bush 30. In FIG. 5 the dashed linesschematically indicate the outer edges of the carrier 4 and the shaft 5.In the embodiment of FIGS. 4 and 5, the bearing bush 30 is provided witha lubrication groove 31 on its radially inner surface having asubstantially elongated shape with a long axis 32, whereby thelubrication groove 31 starts at an axial end 33 of the bearing bush 30closest to the carrier 4 and continues with its long axis 32 oriented atan angle of about 60 degrees with the axial direction, such that itextends in tangential direction in the direction of rotation 50 of thepump shaft. The lubrication groove 31 allows a flow of lubrication fluidin between the pump shaft 5 and the bearing bush, even when the bearingbush 30 fits relatively tightly around said shaft 5. To preventsubstantial fluid communication with the environment, the lubricationgroove 30 ends at some distance from an axial end 34 of the bearing bushopposite the said axial end 33 of the bearing bush 30 closest to thecarrier 4. As indicated in FIG. 5, the bearing bush 30 is oriented suchthat it starts at a tangential position of a discharge section H1 of thepump where the prevailing pressure is at a maximum and it continues intangential direction through a suction section L up to the tangentialposition of a discharge section H2 where the prevailing pressure issmaller than it the first mentioned section H1, so that it extends intangential direction of an angle of about π minus ½π divided by 2, i.e.the number of pump units of the pump of FIG. 3.

[0022] According to the invention the bearing bush 30 may be providedwith a further lubrication groove 35, as is indicated by the dashedlines in FIG. 5. It is further advantageous to provide the radiallyinner surface of the bearing bush 30 with a distribution groove 36having a long axis 37 that is oriented substantially axially andintersecting the long axis 32 of the lubrication groove 31. Thedistribution groove 36 extends over a distance of at about ½ of an axialdimension of the bush 30, but remains at a distance of about ¼ fromeither axial end 33, 34 thereof to limit communication of lubricationfluid between the distribution groove 36 and the environment.

1. Roller vane pump, in particular suited for pumping fluid in acontinuously variable automatic transmission of a motor vehicle,provided with a pump housing (12) accommodating a substantiallycylindrical carrier (4), which is rotatable about a central axis (4 a),and a cam ring (2) encompassing the carrier (4) in the radial direction,and with a pump shaft (5) extending co-axial with said central axis (4a) through the carrier (4), wherein there is provided in the pumphousing (12) a bearing bush (30) having an essentially cylindricalcentral bore through which the pump shaft (5) extends, which bearingbush (30) is provided with a lubrication groove (31) on its radiallyinner surface for allowing fluid to penetrate between the bearing bush(30) and the pump shaft (5), characterised in that the lubricationgroove (31) starts at a tangential position (H1) on the radially innersurface of the bearing bush (30) corresponding to a tangential positionof a discharge section of the roller vane pump, or, when the pump isprovided with more than one discharge sections, to a tangential position(H1) of a discharge section of the roller vane pump where a prevailingfluid pressure is at a maximum during operation of the pump.
 2. Rollervane pump according to claim 1, characterised in that the lubricationgroove (31) has a substantially elongated shape having a long axis (32),whereby the lubrication groove (30) starts at an axial end (33) of thebearing bush (30) closest to th carrier (4) and continues in a directionhaving at least an axial component.
 3. Roller vane pump according toclaim 2, characterised in that the lubrication groove (30) ispredominantly located in a region (L, H1, L) of tangential positions onth radially inner surface of the bearing bush (30) where a contactpressure between the pump shaft (5) and bearing bush (30) is relativelylow, at least during operation of th pump.
 4. Roller vane pump accordingto any of the preceding claims, characterised in that the lubricationgroove tangentially extends from the said tangential position (H1) in adirection of rotation (50) of the pump shaft (5).
 5. Roller vane pumpaccording to any of the preceding claims, characterised in that thelubrication groove (31) is dimensioned such that it tangentially extendsover an angle that approximately corresponds to π minus ½π divided bythe number of pump units of the pump.
 6. Roller vane pump according toclaim 4 or 5, characterised in that the bearing bush is provided with afurther lubrication groove (35) on its radially inner surface, whichfurther lubrication groove (35) starts at an axial end (33) of thebearing bush (30) closest to the carrier (4) and continues in adirection having an axial component, whereby th further lubricationgroove (35) tangentially extends opposite the direction of rotation (50)of the pump shaft (5).
 7. Roller vane pump according to any one of theclaims 1-6, characterised in that the bearing bush (30) is provided witha distribution groove (36) on its radially inner surface, whichdistribution groove (36) has a substantially elongated shape having along axis (37) that is substantially axially oriented and thatintersects the long axis (32) of the lubrication groove (31).
 8. Rollervane pump according to claim 7, characterised in that distribution groov(36) is dimensioned such that it there remains an axial distance betweenthe distribution groove (36) and either axial end (33; 34) of thebearing bush (30) of at least ¼ of an axial dimension of the bearingbush (30).
 9. Roller vane pump according to any of the preceding claims,characterised in that the bearing bush (30) is made of copper or of acopper alloy.
 10. Roller vane pump according to any of the precedingclaims, characterised in that the pump housing (12) is predominantlymade of aluminium.
 11. Roller vane pump according to any of thepreceding claims, characterised in that there is provided in the pumphousing (12) a further bearing bush (30 a), whereby the bearing bush(30) and the further bearing bush (30 a) are each provided on axiallyopposite sides of the carrier (4).
 12. Roller vane pump according to anyof the preceding claims, characterised in that the bearing bush (30) isprovided hook part (38) formed by a radially outwardly orientedthickening that interacts with the pump housing (12) to prevent axialmovement of the bearing bush (30) with respect to the pump housing (12).13. Roller vane pump according to any of the preceding claims, charactrised in that there is provided a cavity (39) that is in communicationwith a pump chamber (13) through a gap between the carrier (4) and thepump housing (12) and with a gap between the bearing bush (30) and thepump shaft (5).
 14. Continuously variable transmission provided with aninput shaft to be drivably connected to an engine, an output shaft to bedrivingly connected to a load and provided with a roller vane pumpaccording to any one of the claims 1-13, wherein the pump shaft (5) isdrivably connected to the engine.